Drive shafts, sometimes also referred to as power take-offs or power trains, frequently snap in conventional heavy duty equipment and vehicles, such as large trucks for hauling heavy loads. Breaks are commonly caused when an excessive load or torque is exerted on the shaft by the prime mover, namely by the engine through the transmission. These breaks are very costly to businesses, resulting in lost productivity, long delays and unnecessary expenses. It takes considerable time to transport such large vehicles to repair shops, to remove and replace the broken drive shafts, and then to return the vehicles to their original work locations. A broken drive shaft can also cause collateral damage to other vehicle parts when it collapses while the vehicle is moving.
Various devices have been proposed to avoid rupture of assorted shafts. The devices link together two parts of the rotatable shaft and provide a means for severing the connection when a certain load condition is reached which is below the breaking point of the shaft. Such prior devices typically employ a form of shear pin connection, examples of which may be found in U.S. Pat. No. 1,637,944 (Keller), U.S. Pat. No. 2,666,394 (Sadler et al), U.S. Pat. No. 2,748,578 (Potts) and U.S. Pat. No. 4,3 18,284 (van der Lely et al).
However, these prior coupling devices suffer from at least some of the following disadvantages. One disadvantage is that linkage to the coupling device requires a shaft ends with a particular configuration or finish, such as a notched spline shaft in van der Lely, a threaded end in Potts or an end with an integral circumferential flange as in Keller. The prior devices are not capable of being connected or retro-fitted onto the end of a plainly cut drive shaft, or would require substantial modification of such shall
Another disadvantage of prior devices is their unsuitability for use with shafts subjected to high r.p.m. (revolutions per minute), namely up to about 2500 r.p.m. Such high speeds require the elements of a coupling device to be balanced about the axis of rotation to avoid wobbling or vibration. The prior devices lack necessary symmetry about the axis of rotation to provide balanced rotation, and so are usually restricted to lower r.p.m., namely up to about 1100 r.p.m., such as in farm bailing machines and tractors. In part this is due to their typically complex construction requiring many individual parts, which also increases manufacturing cost of the devices.
Yet another disadvantage is the difficulty of re-establishing a driving connection between shaft sections upon overload of the coupling devices. Some devices require removal of shrouds or the like before a shear pin member may be accessed. Some allow the shaft sections to loose their axial alignment or to collapse, making it difficult or impossible for a single operator to re-establish a driving connection.
What is desired therefore is a novel device for coupling two sections of a drive shaft which overcomes the limitations and disadvantages of these other prior coupling devices. Preferably it should provide a simple and low cost manner of connecting two sections of a drive shaft for balanced rotation at high r.p.m., and allow for convenient installation on any drive shaft surface without substantial modification or alteration thereof. Preferably it should prevent the drive shaft sections from collapsing upon overload of the coupling device, and should maintain the shaft sections in axial alignment to allow driving connection to be quickly re-established with minimal exertion.